In classical Greek mythology, Zeus, Poseidon and Hades were three brothers who, after defeating the Titans, became the ruling gods of the universe. As it is told in the Iliad, Zeus became the god of the sky, Poseidon the god of the sea and Hades the god of the underworld, with the remaining lot—solid earth—presumed to be the domain available to any of the three, and thus the crux of the rivalry. Their often clever, but generally moody, escapades against each other and with mankind constitute some of the most well-known stories in the hundreds of generations between Homer and Homer Simpson.
Because Zeus is often called the “father of the gods” he is often erroneously thought of as the father of all gods, but this title simply refers to the large amount of godly offspring he sired in his many random sexual conquests; offspring such as Apollo, Athena, Dionysus, Helen of Troy, Hephaestus, Heracles, Hermes, Minos, Persephone, Perseus, among several others. Yet with that established, Poseidon was a playboy in his own right. It was his erotic tryst with Medusa in an Athenian temple that caused her to turn into the hideous beast whom Zeus’s son Perseus beheaded in the movie, Clash of the Titans. He also fathered various other figures such as Polyphemus the Cyclops, who fought Odysseus in the Odyssey, and Triton the Merman, who assisted Jason and his Argonauts in their quest for the Golden Fleece, after Zeus refused to. Hades had less luck than his brothers and is usually featured in tales involving kidnap and/or attempted rape (opposed to successfully executed rape which is sometimes the case with Zeus and Poseidon), most notably with Zeus’s daughter Persephone. The Roman equivalents to Zeus, Poseidon and Hades are Jupiter, Neptune and Pluto.